A. Ramasamy

Altino Loureiro

Antonio Batista

Christopher M. A. Brett

M. J. Marques

R. Martins

Portuguese

Open Repository of the University of Porto

STUDY OF THE INFLUENCE OF POST WELD HEAT TREATMENT (PWHT)  
ON THE SALT SPRAY CORROSION BEHAVIOUR OF 316L STEEL CLAD 
Estoril, Portugal, September 1 - 5, 2013 
ABSTRACT 
Austenitic stainless steels are the most used materials for pressure vessel applications due to their excellent corrosion resistance under diverse service 
conditions. In the present work multilayer steel clads were produced by submerged arc welding (SAW) on plates of carbon steel using electrodes of AISI 309L 
(first layer) and 316L (second and third layers). The thickness of the 3-layer clad is 9.4±0.5 mm. Post-weld heat treatment (PWHT) of the clads was carried out 
using two different conditions. Some of the clads were treated at a temperature of 540 ºC  for 10 h (HT540) and others were treated at 620 ºC for 1 h (HT620). 
Accelerated corrosion tests were conducted using a cyclic corrosion test chamber. Samples of size 70x65x25 mm were cut from NHT, HT540 and HT620; the top 
surfaces were ground and polished to a mirror finish using SiC abrasives and then diamond particles; the side and bottom surfaces were coated by varnish for 
protection. Two salt spray tests were conducted.  
A. Ramasamy1, R. Martins1, M. J. Marques1,2,  A. Batista1, A. Loureiro3 
Christopher M. A. Brett4 
 
1CEMDRX, Department of Physics, University of Coimbra, Portugal 
2Department of Physics Engineering, Faculty of Engineering, University of Porto, Portugal 
3CEMUC, Department of Mechanical Engineering, University of Coimbra, Portugal 
4CEMUC, Department of Chemistry, University of Coimbra, Portugal 
2mjvaz@fe.up.pt, 4cbrett@ci.uc.pt 
Cladding process (Submerged Arc Welding - SAW) 
 Base material: ferritic steel P355 NH  
 1st layer: austenitic stainless steel 309 
 2nd and 3rd layer: austenitic stainless steel 316 L 
 Produced by ARSOPI S.A., Portugal 
Heat treatment parameters after SAW 
 HT540: temperature 540 0C / 10 h 
 HT620: temperature 620 0C / 1 h 
 NHT: non-heat-treated sample 
 
Conclusions 
In Test 1, the surface of NHT presented no significant change, while HT540 and HT620 showed some localized red-brown rust. X-ray diffraction analysis showed 
that the rust consists mainly of α-Fe and α-Fe
2
O
3
; the diffractogram also has peaks of γ-Fe resulting from material adjacent to the rust.  
In Test 2 after the first phase the sample surfaces presented a very small amount of localized red-brown rust. These results confirm that non-heat-treated and 
heat-treated materials possess good corrosion resistance under the tested conditions. However, in test 2 after CCT, the surface of HT620 presented significant 
localized corrosion, NHT showed some localized rust and HT540 insignificant change. 
The results obtained confirm that PWHT at 620 ºC deteriorates the corrosion behaviour of the material under CCT conditions. The partial transformation of 
residual δ-ferrite to σ (a Fe-Cr intermetallic) during the heat treatment produces Cr and Mo deficiency in regions adjacent to the σ phase. As a result, the passive 
film becomes weaker in those regions and leads to localized corrosion. 
ACKNOWLEDGMENTS 
 Financial support of the European Regional Development Fund (ERDF) through "Programa Operacional Factores de Competitividade - COMPETE" and national funds through 
"Fundação para a Ciência e a Tecnologia (FCT)" under the projects Pest-C/FIS/UI0036/2011 and PTDC/EME-TME/103845/2008; 
 Company ARSOPI S.A., Portugal, for providing base materials and welded specimens. 
U. COIMBRA 
TEST 1:The sample surfaces were exposed to a salt spray solution of 1.0±0.1 % 
NaCl, pH 6.5 at a rate of 1-2 ml per 80 cm
2
 per hour at a temperature of 35±2 °C for 
240 h.  
 
TEST 2 was carried out using a solution of 5.0±0.5 % NaCl, pH 6.5 and consisted of 
two phases:  
 first phase: salt spray exposure for 240 h with conditions similar to Test 1; 
 second phase: cyclic corrosion test (CCT), each cycle consisting of the following 
steps: 
            (i) salt spray exposure for 2 h  
            (ii) drying for 4 h at 60 °C and 10 % relative humidity (RH)  
            (iii) exposure for 2 h at 90 % RH at 50 °C. The cycle was repeated 9 times.  
(a
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s 
in
d
ic
a
te
 v
is
ib
le
 r
ed
 c
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si
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 a
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s)
 
Process Equipment 
Accelerated corrosion test 
ARSOPI S.A., Portugal 
Sample surfaces after exposure 
Test 2, after 24 h 
Test 2, after 240 h 
Test 1, after 240 hour 
After the Cyclic Corrosion Test 
Surface before salt spay 
test exposure 
Arrangement of samples 
inside the test chamber 
Salt solution stagnant  
at the bottom of the 
sample 
Typical cross section 
microstructure of all samples 


English

Study of the influence of post weld heat treatment (PWHT) on the salt spray corrosion behaviour of 316L steel clad

Repositório Aberto da Universidade do Porto

STUDY OF THE INFLUENCE OF POST WELD HEAT TREATMENT (PWHT)  ON THE SALT SPRAY CORROSION BEHAVIOUR OF 316L STEEL CLAD Estoril, Portugal, September 1 - 5, 2013 ABSTRACT Austenitic stainless steels are the most used materials for pressure vessel applications due to their excellent corrosion resistance under diverse service conditions. In the present work multilayer steel clads were produced by submerged arc welding (SAW) on plates of carbon steel using electrodes of AISI 309L (first layer) and 316L (second and third layers). The thickness of the 3-layer clad is 9.4±0.5 mm. Post-weld heat treatment (PWHT) of the clads was carried out using two different conditions. Some of the clads were treated at a temperature of 540 ºC  for 10 h (HT540) and others were treated at 620 ºC for 1 h (HT620). Accelerated corrosion tests were conducted using a cyclic corrosion test chamber. Samples of size 70x65x25 mm were cut from NHT, HT540 and HT620; the top surfaces were ground and polished to a mirror finish using SiC abrasives and then diamond particles; the side and bottom surfaces were coated by varnish for protection. Two salt spray tests were conducted.  A. Ramasamy1, R. Martins1, M. J. Marques1,2,  A. Batista1, A. Loureiro3 Christopher M. A. Brett4  1CEMDRX, Department of Physics, University of Coimbra, Portugal 2Department of Physics Engineering, Faculty of Engineering, University of Porto, Portugal 3CEMUC, Department of Mechanical Engineering, University of Coimbra, Portugal 4CEMUC, Department of Chemistry, University of Coimbra, Portugal 2mjvaz@fe.up.pt, 4cbrett@ci.uc.pt Cladding process (Submerged Arc Welding - SAW)  Base material: ferritic steel P355 NH   1st layer: austenitic stainless steel 309  2nd and 3rd layer: austenitic stainless steel 316 L  Produced by ARSOPI S.A., Portugal Heat treatment parameters after SAW  HT540: temperature 540 0C / 10 h  HT620: temperature 620 0C / 1 h  NHT: non-heat-treated sample  Conclusions In Test 1, the surface of NHT presented no significant change, while HT540 and HT620 showed some localized red-brown rust. X-ray diffraction analysis showed that the rust consists mainly of α-Fe and α-Fe2O3; the diffractogram also has peaks of γ-Fe resulting from material adjacent to the rust.  In Test 2 after the first phase the sample surfaces presented a very small amount of localized red-brown rust. These results confirm that non-heat-treated and heat-treated materials possess good corrosion resistance under the tested conditions. However, in test 2 after CCT, the surface of HT620 presented significant localized corrosion, NHT showed some localized rust and HT540 insignificant change. The results obtained confirm that PWHT at 620 ºC deteriorates the corrosion behaviour of the material under CCT conditions. The partial transformation of residual δ-ferrite to σ (a Fe-Cr intermetallic) during the heat treatment produces Cr and Mo deficiency in regions adjacent to the σ phase. As a result, the passive film becomes weaker in those regions and leads to localized corrosion. ACKNOWLEDGMENTS  Financial support of the European Regional Development Fund (ERDF) through "Programa Operacional Factores de Competitividade - COMPETE" and national funds through "Fundação para a Ciência e a Tecnologia (FCT)" under the projects Pest-C/FIS/UI0036/2011 and PTDC/EME-TME/103845/2008;  Company ARSOPI S.A., Portugal, for providing base materials and welded specimens. U. COIMBRA TEST 1:The sample surfaces were exposed to a salt spray solution of 1.0±0.1 % NaCl, pH 6.5 at a rate of 1-2 ml per 80 cm2 per hour at a temperature of 35±2 °C for 240 h.   TEST 2 was carried out using a solution of 5.0±0.5 % NaCl, pH 6.5 and consisted of two phases:   first phase: salt spray exposure for 240 h with conditions similar to Test 1;  second phase: cyclic corrosion test (CCT), each cycle consisting of the following steps:             (i) salt spray exposure for 2 h              (ii) drying for 4 h at 60 °C and 10 % relative humidity (RH)              (iii) exposure for 2 h at 90 % RH at 50 °C. The cycle was repeated 9 times.  (arrows indicate visible red corrosion areas) Process Equipment Accelerated corrosion test ARSOPI S.A., Portugal Sample surfaces after exposure Test 2, after 24 h Test 2, after 240 h Test 1, after 240 hour After the Cyclic Corrosion Test Surface before salt spay test exposure Arrangement of samples inside the test chamber Salt solution stagnant  at the bottom of the sample Typical cross section microstructure of all samples 

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Study of the influence of post weld heat treatment (PWHT) on the salt spray corrosion behaviour of 316L steel clad

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